Calcium/phosphatidylserine-stimulated protein phosphorylation in bone: effect of parathyroid hormone

The calcium/phosphatidylserine (PS)-stimulated phosphorylation of endogenous proteins in the 100,000 x g particulate fraction from neonatal mouse calvaria was investigated. EGTA selectively inhibited the phosphorylation of a 20K protein. The phosphorylation of this 20K protein was stimulated by calcium and by PS. The combination of calcium plus PS increased the phosphorylation of the 20K protein more markedly than either calcium or PS alone. Parathyroid hormone (PTH) (100 nM) treatment of calvaria rapidly altered the phosphorylation of the 20K protein in a time-dependent manner. The PTH treatment time course demonstrated that after 5 minutes the in vitro phosphorylation of the 20K protein was markedly enhanced, after 15 minutes the 20K protein was not as heavily phosphorylated, and after 30 minutes the in vitro phosphorylation of the 20K was less than control. Our results demonstrate the presence of calcium/PS-stimulated phosphorylation in bone tissue and a rapid effect of PTH on this phosphorylation.